Underground fighter Ethan is forced to become mob boss Leon’s “collateral” to save his sister. Cold and ruthless on the surface, Leon secretly protects Ethan and his family. Trained by Leon, Ethan grows stronger but misinterprets Leon’s care for his sister as betrayal. Police mole Noah manipulates Ethan into attempting to kill Leon. At the critical moment, Leon takes a bullet for Ethan, exposing Noah’s true nature. The two reconcile, join forces to eliminate their common enemy Victor, and Leon legitimizes his empire. From hostile rivals to devoted lovers, they become each other’s only cure and destiny.
